Nitride Compounds: Property Anomalies Near Structural Instabilities

非技术描述：该项目正在开发一种新型材料，由两种不同材料的混合物组成，它们被强制结合在一起。这两种物质自然不会混合在一起；然而，如果人工混合，混合物表现出独特的性质，因为一个小的外部刺激可以导致材料结构的大变化。预计这种材料的独特性能包括施加电压或磁场时的强烈变形。例如，这种材料可用于制造一种新型频率滤波器，可将移动设备的数据速率提高10到100倍。这些新特性可能会促进一系列变革性的应用，包括，例如，用于生物医学植入物的磁驱动微开关，核电站中没有任何外部电源或通信通道的应急阀，即使频繁的温度循环也能保持功能的坚韧和弹性涂层（可能应用于高温节油喷气发动机）。技术细节：该项目正在发展对三元氮化物ABN结构不稳定性的理解，其中an和BN形成不同的平衡晶体结构。关键思想是，这种具有中间成分的三元体的单相固溶体表现出结构不稳定性，导致异常的物理性质，包括可逆的塑性变形或发散的压电响应。采用反应溅射法制备了三元氮化物层。外延约束、成分变化和离子表面相互作用用于控制新出现的相、微观结构、织构、应变和可能的相分离。利用原位x射线衍射、拉曼光谱和红外光谱，研究了单相固溶型三元氮化物在高温高压下的结构不稳定性，并确定了结构-应变-能景观。测量了新出现的异常性质，并了解了结构不稳定性如何导致可逆塑性变形、各向异性有效泊松比、压电响应的散度、磁-力耦合和可逆应力诱导的剪切转变。该项目包括对研究生和本科生进行最先进材料合成和表征方面的培训，并参与主要的外联工作，鼓励女孩考虑从事科学和工程方面的职业。

NON-TECHNICAL DESCRIPTION: This project is developing a new type of material consisting of a mixture of two different materials that are forced together. Naturally these two materials would not mix; however, if mixed artificially, the mixture exhibits unique properties because a small external stimulus can lead to a large change in the material structure. The unique properties anticipated for this material include a strong deformation when applying a voltage or a magnetic field. For example such a material is useful for building a new type of frequency filter, which would increase the data rate of mobile devices by ten to hundred times. These new properties may facilitate a whole range of transformative applications, including, for example, magnetically driven micro-switches for biomedical implants, emergency valves in nuclear power plants that operate without any external power source or communication pathway, tough and resilient coatings that remain functional despite frequent temperature cycling (for possible application in high-temperature fuel-efficient jet engines).TECHNICAL DETAILS: This project is developing an understanding of structural instabilities in ternary nitrides ABN where AN and BN form different equilibrium crystal structures. The key idea is that single-phase solid solutions of such ternaries with an intermediate composition exhibit a structural instability that leads to anomalous physical properties, including a reversible plastic deformation or a diverging piezoelectric response. Ternary nitride layers are deposited by reactive sputtering. Epitaxial constraints, composition variations, and ion-surface interactions are used to control the emerging phases, microstructure, texture, strain, and possible phase separation. The structural instabilities of single-phase solid-solution ternary nitrides at elevated temperature and pressure are studied to determine the structure-strain-energy landscape, using in situ x-ray diffraction, Raman and infrared spectroscopies. Emerging anomalous properties are measured and an understanding of how the structural instability leads to a reversible plastic deformation, an anisotropic effective Poisson's ratio, a divergence in the piezoelectric response, a magneto-mechanical coupling, and a reversible stress-induced shear transformation are developed. The project includes training of graduate and undergraduate students in state-of-the-art materials synthesis and characterization, as well as involvement in major outreach efforts to encourage girls to consider a career in science and engineering.